1. Field of the Invention
The present invention relates to a constant velocity joint, and an image forming apparatus that uses the constant velocity joint.
2. Description of the Related Art
Constant velocity joints are used to transmit a rotational torque of a drive shaft of a vehicle to the vehicle shaft. The constant velocity joint transmits the driving force between a driving shaft and a driven shaft that are aligned in an axis direction in a rotational direction at a constant velocity while permitting skew between the two shafts. The constant velocity joint is a drive transmission mechanism that is widely used not only for vehicles but also for various industrial machines.
A typical constant velocity joint includes a first rotation body and a second rotation body that are aligned in the axis direction as disclosed in Japanese Patent Publication No. S52-34699. The first rotation body includes a cup-shape cup unit in which one end in the axis direction in an annular space created between an outer ring and an inner ring inside the outer ring is opened while the other end thereof is closed. In this cup unit, an interior surface of the outer ring and an exterior surface of the inner ring that are opposed to each other through the annular space are provided with a plurality of grooves formed thereon, respectively, the grooves extending in the axis direction and being aligned in a circumferential direction. On the other hand, the second rotation body includes a cylindrical ball holder that is to be inserted into the annular space of the first rotation body. A cylindrical peripheral wall of the ball holder is provided with a plurality of through holes formed thereon so as to be aligned in a circumferential direction, with each of the through holes holding a ball. The second rotation body is inserted into the annular space of the first rotation body in such a manner that these balls are correspondingly engaged with the grooves formed on the interior surface of the outer ring and the exterior surface of the inner ring of the first rotation body. When either one of the first rotation body or the second rotation body rotates as a driving body, the rotational force is transmitted to the other one of the first rotation body or the second rotation body through the plurality of balls that are engaged in the grooves.
Conventionally, the first rotation body and the second rotation body are made of metals so that the constant velocity joint was heavy. Furthermore, the constant velocity joint made loud operation noise due to a friction between the balls and the outer ring or the inner ring. The annular space of the first rotation body is filled with grease for the purpose of a smooth rolling of the balls; however, there is a concern that a leakage of this grease may bring contamination to a surrounding environment. As such, the conventional constant velocity joint was hardly applicable to office machines, acoustic instruments, medical equipments, domestic electric appliances, machines used to manufacture food, or the like.
Thus, there was a need for a constant velocity joint that can be light, less noisy, and that can be in office machines, acoustic instruments, medical equipments, domestic electric appliances, machines used to manufacture food, or the like.